Apparatus and method for communicating and processing a positioning reference signal based on identifier associated with a base station

ABSTRACT

A base station communicates a positioning reference signal (PRS) to wireless communication devices over a downlink in a wireless communication system by encoding a PRS into a first set of transmission resources, encoding other information into a second set of transmission resources, multiplexing the two sets of resources into a subframe such that the first set of resources is multiplexed into at least a portion of a first set of orthogonal frequency division multiplexed (OFDM) symbols based on an identifier associated with the base station and the second set of resources is multiplexed into a second set of OFDM symbols, and transmitting the subframe. Upon receiving the subframe, a wireless device determines which set of transmission resources contains the PRS based on the identifier associated with the base station that transmitted the subframe and processes the set of resources containing the PRS to estimate timing (e.g., time of arrival) information.

FIELD OF THE INVENTION

The present invention relates generally to wireless communicationnetworks and, more particularly, to an apparatus and method forcommunicating and processing positioning reference signals in a downlinksubframe based on an identifier associated with a base stationtransmitting the subframe.

BACKGROUND

Wireless communication networks are well known. Some networks arecompletely proprietary, while others are subject to one or morestandards to allow various vendors to manufacture equipment for a commonsystem. One such standards-based network is the Universal MobileTelecommunications System (UMTS). UMTS is standardized by the ThirdGeneration Partnership Project (3GPP), a collaboration between groups oftelecommunications associations to make a globally applicable thirdgeneration (3G) mobile phone system specification within the scope ofthe International Mobile Telecommunications-2000 project of theInternational Telecommunication Union (ITU). Efforts are currentlyunderway to develop an evolved UMTS standard, which is typicallyreferred to as UMTS Long Term Evolution (LTE) or Evolved UMTSTerrestrial Radio Access (E-UTRA).

According to Release 8 of the E-UTRA or LTE standard or specification,downlink communications from a base station (referred to as an “enhancedNode-B” or simply “eNB”) to a wireless communication device (referred toas “user equipment” or “UE”) utilize orthogonal frequency divisionmultiplexing (OFDM). In OFDM, orthogonal subcarriers are modulated witha digital stream, which may include data, control information, or otherinformation, so as to form a set of OFDM symbols. The subcarriers may becontiguous or discontiguous and the downlink data modulation may beperformed using quadrature phase shift-keying (QPSK), 16-ary quadratureamplitude modulation (16 QAM), or 64 QAM. The OFDM symbols areconfigured into a downlink subframe for transmission from the basestation. Each OFDM symbol has a time duration and is associated with acyclic prefix (CP). A cyclic prefix is essentially a guard periodbetween successive OFDM symbols in a subframe. According to the E-UTRAspecification, a normal cyclic prefix is about five (5) microseconds andan extended cyclic prefix is 16.67 microseconds.

In contrast to the downlink, uplink communications from the UE to theeNB utilize single-carrier frequency division multiple access (SC-FDMA)according to the E-UTRA standard. In SC-FDMA, block transmission of QAMdata symbols is performed by first discrete Fourier transform(DFT)-spreading (or preceding) followed by subcarrier mapping to aconventional OFDM modulator. The use of DFT precoding allows a moderatecubic metric/peak-to-average power ratio (PAPR) leading to reduced cost,size and power consumption of the UE power amplifier. In accordance withSC-FDMA, each subcarrier used for uplink transmission includesinformation for all the transmitted modulated signals, with the inputdata stream being spread over them. The data transmission in the uplinkis controlled by the eNB, involving transmission of scheduling requests(and scheduling information) sent via downlink control channels.Scheduling grants for uplink transmissions are provided by the eNB onthe downlink and include, among other things, a resource allocation(e.g., a resource block size per one millisecond (ms) interval) and anidentification of the modulation to be used for the uplinktransmissions. With the addition of higher-order modulation and adaptivemodulation and coding (AMC), large spectral efficiency is possible byscheduling users with favorable channel conditions.

E-UTRA systems also facilitate the use of multiple input and multipleoutput (MIMO) antenna systems on the downlink to increase capacity. Asis known, MIMO antenna systems are employed at the eNB through use ofmultiple transmit antennas and at the UE through use of multiple receiveantennas. A UE may rely on a pilot or reference symbol (RS) sent fromthe eNB for channel estimation, subsequent data demodulation, and linkquality measurement for reporting. The link quality measurements forfeedback may include such spatial parameters as rank indicator, or thenumber of data streams sent on the same resources; precoding matrixindex (PMI); and coding parameters, such as a modulation and codingscheme (MCS) or a channel quality indicator (CQI). For example, if a UEdetermines that the link can support a rank greater than one, it mayreport multiple CQI values (e.g., two CQI values when rank=2). Further,the link quality measurements may be reported on a periodic or aperiodicbasis, as instructed by an eNB, in one of the supported feedback modes.The reports may include wideband or subband frequency selectiveinformation of the parameters. The eNB may use the rank information, theCQI, and other parameters, such as uplink quality information, to servethe UE on the uplink and downlink channels.

As is also known, present-day cellular telephones include globalpositioning system (GPS) receivers to assist in locating the devices andtheir owners in the event of an emergency and to comply with E-911mandates from the Federal Communication Commission (FCC). Under mostcircumstances, the phone's GPS receiver can receive signals from theappropriate quantity of GPS satellites and convey that information tothe cellular system's infrastructure for determination of the device'slocation by, for example, a location server coupled to or forming partof the wireless network. However, there are some circumstances underwhich the GPS receiver is ineffective. For example, when a user and hisor her cell phone are located within a building, the GPS receiver maynot be able to receive signals from an appropriate quantity of GPSsatellites to enable the location server to determine the device'sposition. Additionally, wireless devices in private systems are notrequired to meet the FCC E-911 mandates and may not include a GPSreceiver. However, circumstances may arise under which determininglocations of wireless devices operating in such systems may benecessary.

To compensate for the intermittent ineffectiveness of the GPS system andto provide location-determining capabilities in private systems, manywireless systems utilize signaling and include processes through which awireless device's location can be estimated. For example, in manysystems, base stations regularly transmit positioning reference signalsthat are received by the wireless devices and used either to determineinformation based upon which an infrastructure device, such as alocation server, can compute (e.g., via triangulation and/ortrilateration) the wireless device's location or to determine thelocation of the wireless device autonomously (i.e., at the wirelessdevice itself). When a location server is intended to compute thewireless device's location, the wireless device may determine time ofarrival (TOA) or time difference of arrival (TDOA) information uponreceiving the positioning reference signal and communicate the TOA orTDOA to the location server via a serving base station (i.e., a basestation providing wireless communication service to the wirelessdevice). The TOA or TDOA information is typically determined based on aninternal clock of the wireless device as established by the wirelessdevice's local oscillator in accordance with known techniques.

Contribution R1-090353 to the 3GPP Radio Access Network (RAN) WorkingGroup 1 (3GPP RAN1) provides one approach for developing downlinksubframes for use in conveying positioning reference signals to UEs inE-UTRA systems. According to Contribution R1-090353, QPSK symbolscontaining the positioning reference signal are distributed throughoutOFDM symbols that are not allocated to control information such that tworesource elements per OFDM symbol carry the positioning referencesymbols. FIG. 1 illustrates exemplary downlink subframes 101, 103transmitted by eNBs serving cells neighboring the cell in which the UEis currently operating. As illustrated, each subframe 101, 103 includesa resource block of twelve subcarriers (sub₀ through sub₁₁), each ofwhich is divided into twelve time segments (to through t₁₁). Each timesegment on a particular subcarrier is a resource element 102, 104, whichcontains a digitally modulated (e.g., QPSK, 16 QAM or 64 QAM) symbol. Aset of resource elements 102, 104 spread across all the subcarriersduring a particular segment or duration of time forms an OFDM symbol. Aset of OFDM symbols (twelve as illustrated in FIG. 1) forms eachsubframe 101, 103.

In the illustrated subframes 101, 103, the first two OFDM symbols ofeach subframe 101, 103 include cell-specific reference symbols (denoted“CRS” in the subframes 101, 103) and other control information (denotedas “C” in the subframes 101, 103) and the remaining OFDM symbols containthe positioning reference signal encoded as symbols into two resourceelements 102 of each OFDM symbol. The resource elements 102, 104containing the positioning reference signal are denoted “PRS” in thesubframes 101, 103. The eNBs transmitting the subframes 101, 103 arecontrolled by one or more controllers in an attempt to maintainorthogonality of the arrangement of the positioning reference signalswithin the non-control portions of the subframes 101, 103 by insuringthat the positioning reference signal symbols are multiplexed intonon-overlapping resource elements 102, 104. Notwithstanding such intentto maintain orthogonality in this manner, the proposed subframestructure may cause a loss of orthogonality under certain conditions.For example, when using a normal cyclic prefix (CP) for each OFDM symbolin the exemplary subframes 101, 103, an inter-site distance (ISD) of 1.5kilometers and a channel delay spread of five microseconds can result ina loss of orthogonality between the different eNB transmitters even whenthey transmit on non-overlapping resource elements 102, 104 asillustrated in FIG. 1. The loss of orthogonality results because theoverall delay spread of the downlink channel (i.e., propagation delayplus multipath delay spread) as seen from the UE exceeds the CP lengthfor normal CP (approximately five microseconds) and, therefore, DFTprecoding is non-orthogonal. For the case of an extended CP(approximately 16.67 microseconds) deployment an ISD of 4.5 km and achannel delay spread of five microseconds can result in loss oforthogonality of subcarrier transmissions.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the one or more embodiments of the present invention.

FIG. 1 is an exemplary downlink subframe for transmitting a positioningreference signal from a base station to a wireless communication devicein accordance with the E-UTRA standard.

FIG. 2 is an electrical block diagram of a wireless communication systemproviding wireless communication service to a wireless communicationdevice in accordance with an exemplary embodiment of the presentinvention.

FIG. 3 illustrates electrical block diagrams of an exemplary basestation usable in the wireless communication system of FIG. 2 and awireless communication device, in accordance with an exemplaryembodiment of the present invention.

FIG. 4 is a logic flow diagram of steps executed by a base station togenerate a downlink subframe for transmission of a positioning referencesignal to a wireless communication device, in accordance with anexemplary embodiment of the present invention.

FIG. 5 illustrates exemplary downlink subframes for communicatingpositioning reference signals to a wireless communication device fromneighbor cell base stations, in accordance with a first exemplaryembodiment of the present invention.

FIG. 6 illustrates exemplary downlink subframes for communicatingpositioning reference signals to a wireless communication device fromneighbor cell base stations, in accordance with a second exemplaryembodiment of the present invention.

FIG. 7 illustrates exemplary downlink subframes for communicatingpositioning reference signals to a wireless communication device fromneighbor cell base stations, in accordance with a third exemplaryembodiment of the present invention.

FIG. 8 is a logic flow diagram of steps executed by a wirelesscommunication device to process a downlink subframe containing apositioning reference signal, in accordance with an exemplary embodimentof the present invention.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale or to include every component of an element. For example,the dimensions of some of the elements in the figures may be exaggeratedalone or relative to other elements, or some and possibly manycomponents of an element may be excluded from the element, to helpimprove the understanding of the various embodiments of the presentinvention.

DETAILED DESCRIPTION

Generally, the present invention encompasses an apparatus and method forcommunicating positioning reference signals based on an identifierassociated with a base station. In accordance with one embodiment, theapparatus is a wireless communication device that includes, inter alia,a receiver and a processor. The receiver is operable to receive at leasta section of one or more subframes, which may or may not be timecontemporaneous, from one or more base stations (e.g., providingwireless communication service to service coverage areas (e.g., cells)adjacent to a service coverage area in which the wireless communicationdevice is located). Each subframe includes transmission resources (e.g.,E-UTRA resource elements) that are divided in time over a symbol acrossa plurality of subcarriers to form a plurality of orthogonal frequencydivision multiplexed (OFDM) symbols. Each transmission resource istransmitted for a predetermined amount of time on a respective one ofthe subcarriers within an OFDM symbol. The OFDM symbols are arrangedinto at least a first set of OFDM symbols that includes a positioningreference signal (e.g., an observed time difference of arrival (OTDOA)waveform) and a second set of OFDM symbols that does not include apositioning reference signal, but which may optionally include acell-specific reference signal, control information (e.g., a PhysicalDownlink Control Channel or PDCCH) and/or data. In one embodiment, eachOFDM symbol of at least the first set has a time duration or occupies atime segment that is identical in length. In such an embodiment, eachOFDM symbol of at least the first set may have a common or identicalcyclic prefix. In another embodiment, a single OFDM symbol may includeall the transmission resources that carry the positioning referencesignal. Additionally, the OFDM symbols which are time adjacent the OFDMsymbol carrying the positioning reference signal may be empty or blankto provide a guard time segment to account for undesired delay spread ofthe downlink channel.

In an alternative embodiment, the first set of OFDM symbols may belogically divided into at least two subsets such that each OFDM symbolof the first subset (e.g., the OFDM symbols having at least onetransmission resource carrying the positioning reference signal) has atime duration greater than each OFDM symbol of the second set having atleast one transmission resource that is not carrying the positioningreference signal. In such an alternative embodiment, the OFDM symbol orsymbols carrying the positioning reference signal may have a cyclicprefix greater than the conventional extended cyclic prefix under theE-UTRA standard (e.g., greater than 16.67 microseconds). Additionally,the transmission resources in the OFDM symbols in the second subset ofthe first set of OFDM symbols may be empty or blank.

In an alternative embodiment, the first set of OFDM symbols may belogically divided into at least two subsets such that each OFDM symbolof the first subset (e.g., the OFDM symbols having at least onetransmission resource carrying the positioning reference signal) has atime duration greater than each OFDM symbol of the second subset of OFDMsymbols. In such an alternative embodiment, the OFDM symbol or symbolscarrying the positioning reference signal may have a cyclic prefixgreater than the conventional extended cyclic prefix under the E-UTRAstandard (e.g., greater than 16.67 microseconds).

The processor is operable to determine, based on an identifierassociated with the base station which transmitted the subframe, a setof transmission resources in which a positioning reference signal wastransmitted, wherein the set of transmission resources constitutes aportion (i.e., some, but not all) of the first set of OFDM symbols. Inother words, the set of transmission resources containing or carryingthe positioning reference signal may be excluded from one or more of theOFDM symbols in the first set of OFDM symbols. The processor is alsooperable to process the set of transmission resources to estimate timinginformation associated with the positioning reference signal.

In one embodiment, the processor is operable to determine a time ofarrival (TOA) of the positioning reference signal based on referencetiming information (e.g., produced from the wireless device's localoscillator) corresponding to a transmission from a particular basestation. Further, the processor may be operable to determine a time ofarrival of the positioning reference signal transmitted from a secondbase station based on reference timing information and to compute a timedifference of arrival (TDOA) of the positioning reference signal fromthe second base station relative to the first base station. In such anembodiment, the wireless communication device may further include atransmitter that is operable to communicate at least one of the time ofarrival and the time difference of arrival to a location server via abase station that is providing wireless communication service to thewireless communication device.

In an alternative embodiment, the apparatus may be a base stationoperable to encode, multiplex, and transmit a downlink subframecontaining a positioning reference signal, a cell-specific referencesignal, and optionally other information, such as control informationand/or data. In such an embodiment, the base station includes, interalia, a processor and a transmitter. The base station processor isoperable to encode a positioning reference signal into a first set oftransmission resources (e.g., E-UTRA resource elements), encodeinformation other than the positioning reference signal into a secondset of transmission resources, and multiplex the first set oftransmission resources and the second set of transmission resources intoa subframe that includes a plurality of OFDM symbols. The base stationtransmitter is operable to transmit to the subframe to wirelesscommunication devices within a coverage range of the base station.

According to one embodiment, the first set of transmission resources ismultiplexed into a portion (i.e., some, but not all, OFDM symbols) of afirst set of OFDM symbols of the subframe (e.g., OFDM symbols forming aportion of the subframe that is not used for transmitting controlinformation (e.g., not forming a PDCCH region) and/or data) based on anidentifier associated with the base station and the second set oftransmission resources is multiplexed into a second set of OFDM symbolsof the subframe (e.g., OFDM symbols used for transmitting controlinformation (e.g., a PDCCH) and/or data). In an alternative embodiment,the processor is further operable to encode data into a third set oftransmission resources and multiplex the third set of transmissionresources into a portion of the second set of OFDM symbols that are notoccupied by the second set of transmission resources. As noted above,the OFDM symbols containing transmission resources carrying thepositioning reference signal may have a time duration and/or a cyclicprefix equivalent to a time duration and/or a cyclic prefix associatedwith the OFDM symbols of the second set. Alternatively, the OFDM symbolscontaining transmission resources carrying the positioning referencesignal may have a time duration and/or a cyclic prefix greater than atime duration and/or a cyclic prefix associated with the OFDM symbols ofthe second set. As a further alternative, the OFDM symbols containingtransmission resources carrying the positioning reference signal mayhave a time duration and/or a cyclic prefix greater than a time durationand/or a cyclic prefix associated with other OFDM symbols of the firstset. Further, the first set of transmission resources may be multiplexedinto the first set of OFDM symbols such that the transmission resourcesare multiplexed onto a subset of the subcarriers forming one or moreOFDM symbols of the first set of OFDM symbols. For example, the firstset of transmission resources may be multiplexed onto one-sixth of thesubcarriers forming an OFDM symbol of the first set of OFDM symbols(e.g., every sixth subcarrier may be used for carrying a transmissionresource corresponding to the positioning reference signal). Stillfurther, a set of blank or empty transmission resources may bemultiplexed into the first set of OFDM symbols such that one or moreOFDM symbols formed by the empty transmission resources is temporallyadjacent an OFDM symbol carrying the positioning reference signal.

By communicating a positioning reference signal to wirelesscommunication devices in this manner, the present invention insuresorthogonality of the OFDM symbols carrying the positioning referencesignals which have been transmitted by base stations of neighboringcells or sectors within a cell even under conditions causing substantialdownlink channel delay spread as perceived by the wireless device.Typically, the base stations (e.g., eNBs) or neighboring base stationsmay coordinate to ensure the wireless devices (e.g., UEs) in the regioncan identify and process the transmitted positioning reference signalsto extract the positioning related information. By utilizing less thanall of the OFDM symbols in a subset (e.g., the non-control channelportion) of the downlink subframe to convey the positioning referencesignal, empty OFDM symbols are made available to absorb the effects ofdelay spreads that are greater than the cyclic prefix of the OFDMsymbols carrying the position reference signal when conventional cyclicprefixes as provided under the E-UTRA standard are used, therebymaintaining the orthogonality of DFT precoding. Alternatively, byincreasing the duration of or cyclic prefix associated with the OFDMsymbol or symbols carrying the positioning reference signal, suchincrease in duration or cyclic prefix offsets increased delay spreadsincurred under various network conditions and enables the orthogonalityof DFT preceding to be maintained.

Embodiments of the present invention can be more readily understood withreference to FIGS. 2-8, in which like reference numerals designate likeitems. FIG. 2 is an electrical block diagram of a wireless communicationsystem 200 providing wireless communication service to one or morewireless communication devices 201 in accordance with an exemplaryembodiment of the present invention. The wireless system 200 includes,inter alia, a plurality of base stations 203-205 (three shown forillustrative purposes), one or more wireless communication devices 201(one shown for illustrative purposes), and an optional location server207. Typically, the wireless system would include many other basestations and wireless communication devices. However, for purposes ofsimplicity in connection with describing the various features of thepresent invention, FIG. 2 depicts only one three base stations 203-205and one wireless communication device 201. In one embodiment, thewireless communication system 200 is a system that implements the E-UTRAstandard. Alternatively, the wireless system 200 may be any system thatutilizes orthogonal frequency division multiplexing and enables wirelessdevices 201 to autonomously determine their location or position withinthe system 200 or absolutely, or assist with such location determinationby, for example, reporting timing information (e.g., time of arrival(TOA) or time difference of arrival (TDOA) information) to the locationserver 207.

The wireless communication device 201 may be implemented as a mobiletelephone, a smart phone, a text messaging device, a handheld computer,a wireless communication card, a personal digital assistant (PDA), anotebook or laptop computer, a consumer premises equipment (CPE), or anyother communication device that has been modified or fabricated toinclude the functionality of the present invention. A smart phone is amobile telephone that has additional application processingcapabilities. For example, in one embodiment, a smart phone is acombination of (i) a pocket personal computer (PC), handheld PC, palmtop PC, or PDA, and (ii) a mobile telephone. Exemplary smart phones arethe iPHONE™ available from Apple, Inc. of Cupertino, Calif. and theMOTOROLA Q™ available from Motorola, Inc. of Schaumburg, Ill. A wirelesscommunication card, in one embodiment, resides or is insertable within aPC or a laptop computer. The term “wireless communication device,” asused herein and the appended claims, is intended to broadly cover manydifferent types of devices that can receive and/or transmit signals andthat can operate in a wireless communication system. For example, andnot by way of limitation, a wireless communication device can includeany one or a combination of the following: a cellular telephone, amobile phone, a smart phone, a two-way radio, a two-way pager, awireless messaging device, a laptop/computer, an automotive gateway, aresidential gateway, a personal computer, a server, a PDA, CPE, arouter, a cordless telephone, a wireless email device, a portable gamingdevice including a built-in wireless modem, and the like. An electricalblock diagram of an exemplary wireless communication device 201 isillustrated in FIG. 3.

The base stations 203-205 provide wireless communication service withinrespective geographic service coverage areas (e.g., cells). The basestations 203-205 may be co-located or diversely located. Whenco-located, the base stations 203-205 may provide wireless service torespective portions (e.g., sectors) of a single service coverage area(e.g., a cell). In one embodiment, the base stations are eNBs thatoperate in accordance with the E-UTRA standard.

The location server 207 is well known and is used to determine locationsof wireless communication devices 207 within the wireless communicationsystem 200. In one embodiment, the location server 207 usestriangulation or trilateration to locate a wireless communication device201 based on known locations of base stations 203-205 within the system200 together with time of arrival or time difference of arrivalmeasurements made and reported by the wireless communication device 201in response to receiving subframes carrying positioning referencesignals 209-211 from the base stations 203-205. Locations determined bythe location server 207 may be used for a variety of reasons, includingto locate a wireless device that has made an emergency call when suchdevice does not include GPS functionality or when GPS functionality isinoperable or impaired for any reason. While the location server 207 isshown a distinct entity from the base stations 203-205, it is notnecessary as certain base stations can also provide the logicalfunctionality of a location server 207.

FIG. 3 illustrates electrical block diagrams of the wirelesscommunication device 201 and an exemplary base station 301 usable in thewireless communication system 200 of FIG. 2. The base station 301 may beused to implement any of the base stations 203-205 of the wirelesscommunication system 200 of FIG. 2. Each base station 301 includes,inter alia, one or more transmit antennas 304-307 (four shown forillustrative purposes), one or more receive antennas 309, 310 (two shownfor illustrative purposes), one or more transmitters 312 (one shown forillustrative purposes), one or more receivers 314 (one shown forillustrative purposes), one or more processors 316 (one shown forillustrative purposes), and memory 318. Although illustrated separately,the transmitter 312 and the receiver 314 may be integrated into one ormore transceivers as is well understood in the art. By includingmultiple transmit antennas 304-307 and other appropriate hardware andsoftware as would be understood by those of ordinary skill in the art,the base station 301 may support use of a multiple input and multipleoutput (MIMO) antenna system for downlink (base station-to-wirelesscommunication device) communications. The MIMO system facilitatessimultaneous transmission of downlink data streams from multipletransmit antennas 304-307 depending upon a channel rank, for example asindicated by the wireless communication device 201 or as preferred bythe base station 301. A rank supplied by the wireless communicationdevice 201 assists or enables the base station 301 to determine anappropriate multiple antenna configuration (e.g., transmit diversity,open loop spatial multiplexing, closed loop spatial multiplexing, etc.)for a downlink transmission in view of the current downlink channelconditions.

The processor 316, which is operably coupled to the transmitter 312, thereceiver 314, and the memory 318, can be one or more of amicroprocessor, a microcontroller, a digital signal processor (DSP), astate machine, logic circuitry, any combination thereof, or any otherdevice or combination of devices that processes information based onoperational or programming instructions stored in the memory 318. One ofordinary skill in the art will appreciate that the processor 316 can beimplemented using multiple processing devices as may be required tohandle the processing requirements of the present invention and thevarious other functions of the base station 301. One of ordinary skillin the art will further recognize that when the processor 316 has one ormore of its functions performed by a state machine or logic circuitry,the memory containing the corresponding operational instructions can beembedded within the state machine or logic circuitry as opposed to beingexternal to the processor 316.

The memory 318, which may be a separate element as depicted in FIG. 3 ormay be integrated into the processor 316, can include random accessmemory (RAM), read-only memory (ROM), FLASH memory, electricallyerasable programmable read-only memory (EEPROM), removable memory, ahard disk, and/or various other forms of memory as are well known in theart. The memory 318 can include various components, such as, forexample, one or more program memory components for storing programminginstructions executable by the processor 316, one or more address memorycomponents for storing an identifier associated with the base station301 as well as for storing addresses for wireless communication devicescurrently in communication with the base station 301, and various datastorage components. The identifier may be derived from at least one ofan offset identifier specific to the base station, a base stationidentifier, a cell site identifier, a physical cell identifier, a globalcell identifier, a slot index, a subframe index, a system frame number,and/or a radio network transaction identifier. The program memorycomponent of the memory 318 may include a protocol stack for controllingthe transfer of information generated by the processor 316 over the dataand/or control channels of the system 200. It will be appreciated by oneof ordinary skill in the art that the various memory components can eachbe a group of separately located memory areas in the overall oraggregate memory 318 and that the memory 318 may include one or moreindividual memory elements.

In one embodiment, the base station transmitter 312, receiver 314, andprocessor 316 are designed to implement and support a wideband wirelessprotocol, such as the Universal Mobile Telecommunications System (UMTS)protocol, the E-UTRA protocol, the 3GPP Long Term Evolution (LTE)protocol, or a proprietary protocol, operating to communicate digitalinformation, such as user data (which may include voice, text, video,and/or graphical data) and/or control information, between the basestation 301 and the wireless communication device 201 over various typesof channels. In an E-UTRA system, an uplink data channel may be a PUSCH,an uplink control channel may be a physical uplink control channel(PUCCH), a downlink control channel may be a physical downlink controlchannel (PDCCH), and downlink data channel may be a physical downlinkshared channel (PDSCH). Uplink control information may be communicatedover the PUCCH and/or the PUSCH and downlink control information iscommunicated typically over the PDCCH.

When the base station 301 implements the E-UTRA standard, the basestation processor 316, in one embodiment, includes a logical channelcoding and multiplexing section for implementing channel coding andmultiplexing of control information, positioning reference signals, anddata destined for transmission over a downlink subframe 340. Severaltypes of downlink channels may be combined into a single downlinksubframe 340 as described in more detail below with respect to FIGS.5-7. The channel coding and multiplexing section is a logical section ofthe base station processor 316, which performs the coding andmultiplexing responsive to programming instructions stored in memory318. The channel coding and multiplexing section may include one channelcoding block for encoding control channel information (e.g., channelquality indicators, cell-specific reference symbols (CRS), rankindicators, and hybrid automatic repeat request acknowledgments(HARQ-ACK/NACK) into associated transmission resources (e.g.,time-frequency resource elements), another block for encodingpositioning reference signals and other information typicallycommunicated over the primary/secondary synchronization channel (e.g.,P/S-SCH) into associated transmission resources, and a further channelcoding block for encoding data into data channel (e.g., PDSCH)transmission resources. The channel coding and multiplexing section ofthe processor 316 may include additional coding blocks for encodingvarious other types of information and/or reference symbols used by thewireless communication device 201 for demodulation and downlink channelquality determination. The channel coding and multiplexing section ofthe processor 316 also includes a channel multiplexing block thatmultiplexes the encoded information generated by the various channelcoding blocks into a subframe, which is supplied to the transmitter 312for downlink transmission.

Each wireless communication device 201 includes, inter alia, one or moretransmit antennas 320 (one shown for illustrative purposes), one or morereceive antennas 322, 323 (two shown for illustrative purposes), one ormore transmitters 325 (one shown for illustrative purposes), one or morereceivers 327 (one shown for illustrative purposes), a processor 329,memory 331, a local oscillator 332, an optional display 333, an optionaluser interface 335, and an optional alerting mechanism 337. Althoughillustrated separately, the transmitter 325 and the receiver 327 may beintegrated into one or more transceivers as is well understood in theart. By including multiple receive antennas 322, 323 and otherappropriate hardware and software as would be understood by those ofordinary skill in the art, the wireless communication device 201 mayfacilitate use of a MIMO antenna system for downlink communications.

The wireless communication device transmitter 325, receiver 327, andprocessor 329 are designed to implement and support a wideband wirelessprotocol, such as the UMTS protocol, the E-UTRA protocol, the 3GPP LTEprotocol or a proprietary protocol, operating to communicate digitalinformation, such as user data (which may include voice, text, video,and/or graphical data) and/or control information, between the wirelesscommunication device 201 and a serving base station 301 over control anddata channels. In an E-UTRA system, an uplink data channel may be aPUSCH and an uplink control channel may be a PUCCH. Control informationmay be communicated over the PUSCH and/or the PUCCH. Data is generallycommunicated over the PUSCH.

The processor 329 is operably coupled to the transmitter 325, thereceiver 327, the memory 331, the local oscillator 332, the optionaldisplay 333, the optional user interface 335, and the optional alertingmechanism 337. The processor 329 utilizes conventional signal-processingtechniques for processing communication signals received by the receiver327 and for processing data and control information for transmission viathe transmitter 325. The processor 329 receives its local timing andclock from the local oscillator 332, which may be a phase locked looposcillator, frequency synthesizer, a delay locked loop, or other highprecision oscillator. The processor 329 can be one or more of amicroprocessor, a microcontroller, a DSP, a state machine, logiccircuitry, or any other device or combination of devices that processesinformation based on operational or programming instructions stored inthe memory 331. One of ordinary skill in the art will appreciate thatthe processor 329 can be implemented using multiple processors as may berequired to handle the processing requirements of the present inventionand the various other included functions of the wireless communicationdevice 201. One of ordinary skill in the art will further recognize thatwhen the processor 329 has one or more of its functions performed by astate machine or logic circuitry, the memory containing thecorresponding operational instructions can be embedded within the statemachine or logic circuitry as opposed to being external to the processor329.

The memory 331, which may be a separate element as depicted in FIG. 3 ormay be integrated into the processor 329, can include RAM, ROM, FLASHmemory, EEPROM, removable memory (e.g., a subscriber identity module(SIM) card or any other form of removable memory), and/or various otherforms of memory as are well known in the art. The memory 331 can includevarious components, such as, for example, one or more program memorycomponents for storing programming instructions executable by theprocessor 329 and one or more address memory components for storingaddresses and/or other identifiers associated with the wirelesscommunication device 201 and/or the base stations 203-205. The programmemory component of the memory 331 may include a protocol stack forcontrolling the transfer of information generated by the processor 329over the data and/or control channels of the system 200, as well as forcontrolling the receipt of data, control, and other informationtransmitted by the base stations 203-205. It will be appreciated by oneof ordinary skill in the art that the various memory components can eachbe a group of separately located memory areas in the overall oraggregate memory 331 and that the memory 331 may include one or moreindividual memory elements.

The display 333, the user interface 335, and the alerting mechanism 337are all well-known elements of wireless communication devices. Forexample, the display 333 may be a liquid crystal display (LCD) or alight emitting diode (LED) display and associated driver circuitry, orutilize any other known or future-developed display technology. The userinterface 335 may be a key pad, a keyboard, a touch pad, a touch screen,or any combination thereof, or may be voice-activated or utilize anyother known or future-developed user interface technology. The alertingmechanism 337 may include an audio speaker or transducer, a tactilealert, and/or one or more LEDs or other visual alerting components, andassociated driver circuitry, to alert a user of the wirelesscommunication device 302. The display 333, the user interface 335, andthe alerting mechanism 337 operate under the control of the processor329.

Referring now to FIGS. 2-7, operation of a base station 301 (which maybe any of the base stations 203-205 in the exemplary wireless system200) occurs substantially as follows in accordance with the presentinvention. At a predetermined time (e.g., periodically oraperiodically), the base station processor 316 optionally encodes (401)control information into a first set of transmission resources of areference block of transmission resources allocated for transmission.Where the base station 301 implements the E-UTRA or LTE standard, theallocated block of transmission resources includes time-frequencyresource elements to be multiplexed into a subframe of OFDM symbolsforming one or more transmission channels. For each transmit antenna,the set of transmission resources form a two-dimensional resourceelement grid in time and frequency. In frequency, the transmissionresources are typically mapped into different subcarriers within eachOFDM symbol across the transmission bandwidth. Multiple such OFDMsymbols comprise a subframe. In the E-UTRA standard, at least twosubframe structures—one with 14 OFDM symbols referred to as a “normal CPsubframe” and one with 12 OFDM symbols referred to an “extended CPsubframe”—are defined. The subframe may be further divided into twohalves or slots with an equal number of OFDM symbols. A subframe maycarry one or more transmission channels such as control channel (e.g.,PDCCH, PCFICH, PHICH), data channel (e.g., PDSCH), broadcast channel(e.g., PBCH), synchronization channel (e.g., P/S-SCH), or any otherchannel. In addition to these channels, the subframe may include acell-specific reference signal, a dedicated or UE-specific referencesignal, a positioning reference signal, or any other reference signal.

In E-UTRA, there are two types of subframes—a unicast subframe where theCell-specific Reference symbols are sent in both the slots of thesubframe, Some other subframes may be occasionally characterized asspecial sub-frames or non-unicast subframes. For example, MultimediaBroadcast Multicast Service over a Single Frequency Network (MBSFN)subframes, wherein the subframe structure is different from a unicastsubframes. In the special subframes or non-unicast subframes, the firstone or two (or possibly zero) OFDM symbols may contain the PDCCH andreference symbols, whereas the rest of the subframe including the RSstructure may be different than a unicast subframe. For instance, themultimedia multicast broadcast over single frequency network (MBSFN)subframe is a type of non-unicast subframe wherein the rest of thesubframe may be blanked or empty and these empty resources can be usedto transmit positioning reference symbols. The non-unicast (or specialsubframe) signaling pattern may be part of system configuration orSystem Information Broadcast (SIB) message and may be defined on aRadio-frame level (10 subframes) or for a group of Radio Frame level. Inone embodiment, the base station processor 316 encodes controlinformation into resource elements to be multiplexed into a portion ofthe first two OFDM symbols of the subframe.

The coded control information may include downlink assignments or uplinkgrants, control channel duration, and hybrid automatic repeat requestacknowledgments (HARQ-ACK/NACK). In addition to the control information,a set of symbols corresponding to a cell-specific reference signal maybe included in the subframe. The cell-specific reference signal may beused for channel estimation, demodulation, delay tracking,mobility-related measurements, and other purposes by the wireless device201. When included, the sequence of symbols corresponding to the cellspecific reference signal and the time-frequency locations occupied bythe symbols may be derived from an identifier associated with the basestation 301. Such identifier may include a physical cell identifier(PCID), a slot index and/or a symbol index, all of which are well knownin the art particularly in connection with the E-UTRA standard. Inaddition, the subcarrier offset used for mapping the symbols of thecell-specific reference signal into an OFDM symbol may be derived fromthe physical cell identifier.

In addition to optionally encoding control information and thecell-specific reference signal into transmission resources, the basestation processor 316 encodes (403) a positioning reference signal intoa second set of transmission resources. The base station processor 316encodes the positioning reference signal into a portion of a pluralityof resource blocks where each resource block comprises a two-dimensionalgrid of approximately 12 contiguous subcarriers in frequency and all theOFDM symbols of the subframe in time where each OFDM symbol isassociated with a normal or an extended cyclic prefix as described inthe E-UTRA standard. For illustration purposes, a typical resource blockis defined as the resources available in 12 subcarriers and all OFDMsymbols of the subframe. It is noted that the resource block dimensionsmay be varying as some of the subcarriers of OFDM symbols may be usedfor other purposes such as transmission of pre-determined controlprimary broadcast channel, or synchronization channels, etc. The numberof resource blocks available for transmission on the downlink (i.e., thelink between the base station 301 and wireless device 201) may bedependent on the transmission bandwidth. The base station processor 316may be programmed to encode the positioning reference signal into asubset of the available OFDM symbols in the subframe. In one exemplaryembodiment, the base station processor 316 encodes the positioningreference signal into a portion of 600 resource elements of an OFDMsymbol of the subframe when the downlink transmission bandwidth is 10MHz. Further, not all of the subcarriers on these OFDM symbols may beused for carrying the transmission resources corresponding to thepositioning reference signal. In one example, every sixth subcarrier isused for transmitting the symbols of the positioning reference signal.In such an exemplary embodiment, the single OFDM symbol carrying thepositioning reference signal may have a cyclic prefix greater than thecyclic prefixes associated with other OFDM symbols in the non-controlchannel portion of the subframe. For example, the cyclic prefixassociated with the single OFDM symbol carrying the positioningreference signal may be greater than 16.67 microseconds, the extendedcyclic prefix provided under the E-UTRA standard, and, in oneembodiment, is 25 microseconds. Of course, those of ordinary skill inthe art will readily recognize and appreciate that the positioningreference signal may be encoded into various other quantities oftransmission resources and still remain within the scope of the presentinvention.

In one embodiment, the transmission resources carrying the controlinformation (e.g., control channel or PDCCH) and the positioningreference signal constitute less than all the transmission resourcesavailable for transmission. As a result, the base station processor 316may optionally encode (405) data into a third set of transmissionresources to utilize a portion of the subframe for transmission.

The base station processor 316 may optionally encode the controlinformation coded into the first set of transmission resources and, inone embodiment, may encode the positioning reference signal, and anyoptional data into their respective sets of transmission resources. Thebase station processor 316 may multiplex (407) the transmissionresources containing the control information into OFDM symbols in acontrol channel portion (e.g., PDCCH over the first two OFDM symbols) ofa subframe. Additionally, the base station processor 316 multiplexes(409) the transmission resources containing the positioning referencesymbols into OFDM symbols in a part or a portion of a non-controlchannel portion of the subframe. In other words, in contrast to thesubframe structure illustrated in FIG. 1 as proposed in Contribution No.R1-090353 to the 3GPP Radio Access Network (RAN) Working Group 1 (3GPPRAN1), in which the positioning reference signal (PRS) is multiplexedinto two resource elements of each OFDM symbol in the non-controlchannel portion of a subframe within a resource block, the base stationprocessor 316 multiplexes the positioning reference signal resourcesinto only part of the non-control channel portion of the subframeleaving at least one of the OFDM symbols in the non-control channelportion of the subframe either empty or available for other information,such as a data transmission. In one embodiment, the base stationprocessor 316 optionally multiplexes (411) one or more empty or blankOFDM symbols into the non-control portion of the subframe so as to betemporally adjacent an OFDM symbol carrying positioning reference signaltransmission resources. For example, the base station processor 316 maymultiplex multiple empty OFDM symbols into the non-control portion ofthe subframe such that at least one empty OFDM symbol is positionedimmediately preceding the OFDM symbol carrying the positioning referencesignal transmission resources and such that at least one empty OFDMsymbol is positioned immediately succeeding the OFDM symbol carrying thepositioning reference signal transmission resources. Such an exemplaryembodiment effectively provides guard periods around the OFDM symbolcarrying the positioning reference signal transmission resources when acyclic prefix of such OFDM symbol is normal or extended as provided inthe E-UTRA standard so as to mitigate the effects of downlink channeldelay spread when such delay spread exceeds the cyclic prefix of theOFDM symbol. The use of empty or blank OFDM symbols adjacent an OFDMsymbol carrying positioning reference signal transmission resourcesfurther helps to insure orthogonality between subframe transmissionsfrom base stations serving neighboring service coverage areas (e.g.,cells or sectors) as described in more detail below with respect to FIG.5.

In addition to optionally multiplexing the control informationtransmission resources, the cell-specific reference signal and thepositioning reference signal transmission resources into OFDM symbols ofthe subframe, the base station processor 316 multiplexes (413) alloptionally-included data transmission resources into remaining OFDMsymbols in the non-control portion of the subframe (i.e., into a datachannel, such as a PDSCH) when the processor 316 is programmed toinclude such data in the subframe. In one embodiment, the data resourcesare multiplexed into a subset of OFDM resources in the non-controlportion of the subframe that are mutually exclusive of the OFDM symbolscarrying the positioning reference signal resources. For example, thedata resources may be multiplexed into a set of one or more OFDM symbolsthat is separated in time by at least one OFDM symbol from the OFDMsymbol or symbols carrying the positioning reference signal resources.Alternatively, the data resources may be multiplexed into a set of OFDMsymbols that are temporally adjacent the OFDM symbol or symbols carryingthe positioning reference signal resources. Exemplary subframescontaining coded positioning reference signals multiplexed into OFDMsymbols as produced by base station processors 316 implementingembodiments of the present invention are illustrated in FIGS. 5-7. Afterthe entire block of transmission resources have been multiplexed intothe subframe, the base station transmitter transmits (415) the subframevia one or more of the antennas 304-307.

Although the encoding of the control information, the positioningreference signal, and any optional data have been shown in one exemplaryorder in FIG. 4, those of ordinary skill in the art will readilyrecognize and appreciate that the coding order may be changed as sodesired and is not critical to the present invention. Similarly,although the multiplexing of the control information resources, thepositioning reference signal resources, and the data resources (whenincluded) have been shown in one exemplary order in FIG. 4, those ofordinary skill in the art will readily recognize and appreciate that themultiplexing order may be changed as so desired and is not critical tothe present invention.

FIGS. 5-7 illustrate exemplary downlink subframes 501-502, 601-602,701-702 in an E-UTRA or LTE system for communicating positioningreference signals to wireless communication devices 201, in accordancewith exemplary embodiments of the present invention. In the exemplarysubframes 501-502, 601-602, 701-702, “C” represents channel-codedcontrol information symbols, “CRS” represents cell-specific referencesymbols, “PRS” represents positioning reference symbols, and “D”represents channel-coded data symbols.

Referring first to FIG. 5, such figure depicts subframes 501, 502generated and transmitted by base stations providing communicationservice to service coverage areas (e.g., cells or cell sectors) adjacentto or neighboring the service coverage area in which the wirelesscommunication device 201 receiving the subframes is located. Forexample, in the wireless system 200 illustrated in FIG. 2, if basestation 204 is supplying communication service to the wireless device201 (i.e., the wireless device 201 is located in the service coveragearea of base station 204 and, therefore, base station 204 is the servingstation for the wireless device 201), then the service coverage areasserviced by base stations 203 and 205 may be considered neighboringservice coverage areas and base stations 203 and 205 may be consideredneighboring base stations. One of ordinary skill in the art will readilyappreciate and recognize that the quantity of neighboring servicecoverage areas and base stations may exceed to the two illustrated inFIG. 2. Accordingly, the approach disclosed herein for subframe creationmay be used by every base station in the applicable wireless systembecause, at some point in time, each base station serves a servicecoverage area neighboring a service coverage area in which at least onewireless communication device is located.

According to the present invention, the base station processors 316generate their subframes 501, 502 so as to achieve and maintainorthogonality of the positioning reference symbols in the presence ofvarious downlink channel conditions. In the subframe structureembodiments illustrated in FIG. 5, the base station processors 316 areprogrammed to map or multiplex resource elements 503, 506 containingcontrol information bits into the first two OFDM symbols of the subframe501, 502 (e.g., the OFDM symbols corresponding to time segments t₀ andt₁ of each subframe 501, 502). Such OFDM symbols may be considered toform the control channel (e.g., PDCCH) portion or the control region ofthe subframe 501, 502. The base station processors 316 are furtherprogrammed to multiplex resource elements 504, 507 containing thepositioning reference signal and resource elements 505, 508 containingchannel-coded data bits (when included) into the remaining OFDM symbolsof the subframe, which constitute the non-control channel portion of thesubframe 501, 502. Thus, the resource elements 504, 507 containing thepositioning reference signal are multiplexed into less than all the OFDMsymbols in the non-control channel portion of the subframe 501, 502. Inthe absence of data, the resource elements 505, 508 allocated for datapayload may be empty or blank. When data is included, the non-controlchannel portion of the subframe is effectively divided into two or moresubsets, one subset containing the OFDM symbols carrying the positioningreference signal and the other subset(s) containing empty OFDM symbols,data, and/or other information.

When a positioning reference signal is to be included, the resourceelements for carrying the positioning reference signal may be allocatedin either a pre-determined fashion (e.g., as defined in the E-UTRA orLTE standards), semi-statically through broadcast (e.g. via signaling ina master information block (MIB) or system information block (SIB)) orin a user-specific message (e.g., radio resource control measurementconfiguration message), dynamically (e.g., via control channel signalingin PDCCH), or by higher layer signaling (e.g., location server protocoldata units). In the exemplary subframes 501, 502 of FIG. 5, the durationof and cyclic prefix associated with each OFDM symbol of the subframe isidentical. In alternative embodiments, such as the embodiment disclosedbelow with respect to FIG. 7, the OFDM symbols carrying the positioningreference signal may have a longer duration and be associated with agreater cyclic prefix than the other OFDM symbols in at least thenon-control channel portion of the subframe 501, 502. In the exemplarysubframes 501, 502 of FIG. 5, the control region of the subframecomprises two OFDM symbols. In alternative embodiments, the controlregion may comprise one OFDM symbol or three OFDM symbols. In theexemplary subframes 501, 502 of FIG. 5, the last five OFDM symbols mayoptionally contain a data transmission. In alternative embodimentseither no OFDM symbol may be allocated for data transmission or adifferent number of OFDM symbols may be allocated for data transmission.The portion of the non-control region that may contain data transmissionmay be pre-determined (e.g., specified in a 3GPP specification) orindicated to the UE in semi-statically in a broadcast message (e.g.,master information block or system information block) or through higherlayer signaling.

In the embodiment illustrated in FIG. 5, the resource elements 504, 507containing the respective positioning reference signals are mapped ormultiplexed onto different OFDM symbols, thereby achievingorthogonality. For example, the resource elements 504 containing thepositioning reference signal transmitted by a first neighbor basestation (e.g., base station 203) may be multiplexed into the fifth OFDMsymbol at time segment t₄ of subframe 501. By contrast, the resourceelements 507 containing the positioning reference signal transmitted bya second neighbor base station (e.g., base station 205) may bemultiplexed into the seventh OFDM symbol at time segment t₆ of subframe502. The subframes 501, 502 may be contemporaneous or offset in time. Inone embodiment, the mapping of which OFDM symbol of the subframe 501,502 contains the positioning reference signal is based on an identifierassociated with the base station 203, 205, which may take into accountthe base station's location in the system 200 and the reuse pattern ofthe various subcarriers used to generate OFDM symbols of the subframe.The identifier may be one or more of an offset identifier, a basestation identifier, a cell site identifier, a physical cell identifier(PCID), a global cell identifier (GCID), a symbol index, a slot index, asubframe index, a system frame number (SFN), and/or a radio networktransaction identifier (RNTI). In the exemplary subframes 501, 502 ofFIG. 5, the resource elements 505, 507 containing data bits, whenincluded, are multiplexed into the last five OFDM symbols of thesubframe 501, 502, thereby forming a data channel (e.g., PDSCH) portionof the subframe 501, 502.

To further increase the likelihood that orthogonality of the positioningreference symbols is maintained under all downlink channel conditions,the OFDM symbols which two neighboring base stations are allowed to useto communicate positioning reference signal resource elements 504, 507are separated by at least one OFDM symbol such that|l_(offset,2)−l_(offset,1)|≧2, where l_(offset,1) is the symbol positionin subframe 501 of the OFDM symbol carrying the positioning referencesignal resource elements 504 transmitted by one neighbor base station(e.g., base station 203) and l_(offset,2) is the symbol position insubframe 502 of the OFDM symbol carrying the positioning referencesignal resource elements 507 transmitted by the other neighbor basestation (e.g., base station 205). Separation of the two OFDM symbolscarrying the positioning reference signal resource elements 504, 507 byat least one ODFM symbol is preferable to preserve orthogonality betweentransmissions from different base stations (e.g., serving two differentsectors or two neighboring cells) when the sum of the propagation delaybetween the base station transmitters 312 and the multipath delay spreadof the propagation channel exceeds the cyclic prefix length associatedwith the OFDM symbols carrying the positioning reference signal resourceelements 504, 507. In a synchronous network, such orthogonality can beachieved in an uncoordinated fashion by, for example, setting the OFDMsymbol position offset as a function of an identifier associated withthe base station 203, 205 that is transmitting the subframe 501, 502.For example, the symbol position of the OFDM symbol carrying thepositioning reference signal resource elements 504, 507 may bedetermined as l_(offset,ID)=ƒ(ID)=mod(2 ID+2,12), where the identifierassociated with the base station transmitting the subframe 501, 503 (ID)may be derived from one or more of a physical cell identifier (PCID), abase station identifier, a cell site ID, a global cell identifier(GCID), a system frame number (SFN), a symbol index, a slot index, asubframe index, a radio network transaction identifier (RNTI) or anyother applicable identifier. In this example, two consecutiveidentifiers (e.g., ID and ID+1) are associated with two neighboring basestations in a synchronous deployment, it would result in gap betweensuch transmissions of the positioning reference signal from the twotransmitter ensuring orthogonality. The functional ƒ(·) can be a genericfunction (e.g., a pre-determined mapping specified in a 3GPPspecification or a pseudo-random mapping) or a mapping thatorthogonalizes positioning reference signal transmissions from two basestations with different identifiers.

The positioning reference signals (e.g., observed time difference ofarrival (OTDOA) waveforms) from neighboring base stations 203, 205 canbe used jointly such that there is time-domain separation betweentransmissions of such signals from neighboring base stations 203, 205.Further, not all of the subcarriers or resource elements on the OFDMsymbols carrying the positioning reference signal may be used fortransmission. The set of resource elements carrying the positioningreference signal in an OFDM symbol may determined as a function of anidentifier associated with the transmitting base station which may bederived from at least one of a physical cell identifier (PCID), a basestation identifier, a cell site ID, a global cell identifier (GCID), asystem frame number (SFN), a symbol index, a slot index, a subframeindex, a radio network transaction identifier (RNTI) or any otherapplicable identifier. In one embodiment, P/S-SCH extension techniquescan be used to multiplex resource elements across a bandwidth of thesubframes 501, 502 for the OFDM symbols used by the base stations 203,205 to communicate the positioning reference signals.

To enhance the timing extraction support from the positioning referencesignal, the sequence of symbols used for encoding the transmissionresources corresponding to the positioning reference signal may begenerated in a way to avoid secondary cross-correlation peaks. A Goldsequence generators may be used for generating an in-phase (I) streamand a quadrature (Q) stream of and a QPSK sequence may be constructedfrom the I-Q streams. The initializers or the seeds for the registers inthe Gold sequence generator may be derived from an identifier associatedwith the base station. The identifier may be derived from at least oneof a physical cell identifier (PCID), a base station identifier, a cellsite ID, a global cell identifier (GCID), a system frame number (SFN), asymbol index, a slot index, a subframe index, a radio networktransaction identifier (RNTI) or any other applicable identifier.Further, such an identifier may be used to derive an offset that is usedas the starting point of extraction of a subsequence from the so-derivedQPSK sequence. This QPSK sequence may then be used for encoding thetransmission resources used for transmitting the positioning referencesignal. In another example, an orthogonal set of time-frequencyresources for transmission of positioning reference symbols (PRS) may beidentified for use in a set of coordinating base stations. Thus,coordinating base stations can orthogonalize their PRS transmissions byselecting different indices into the orthogonal set of time-frequencyresources and this index may also be considered as part of theidentifier.

In one embodiment, to further aid in preserving orthogonality when OFDMsymbols carrying positioning reference signal resource elements 504, 507are transmitted by neighboring base stations 203, 205 and are separatedby at least one ODFM symbol, blank or empty resource elements 509, 510are multiplexed into one or more of the OFDM symbols immediatelyadjacent the OFDM symbols carrying the positioning reference symbols.For example, as illustrated in subframe 501, blank resource elements 509are multiplexed into the fourth and sixth OFDM symbols adjacent to thefifth OFDM symbol, which is carrying the positioning reference signalresource elements 504. Similarly, as illustrated in subframe 502, blankresource elements 510 are multiplexed into the sixth and eighth OFDMsymbols adjacent to the seventh OFDM symbol, which is carrying thepositioning reference signal resource elements 507. In a furtherembodiment, blank or empty resource elements 509, 510 may also bemultiplexed into an OFDM symbol corresponding to the OFDM symbolcarrying a positioning reference signal of a neighboring base station.For example, one base station 203 may multiplex empty resource elements509 into the seventh OFDM symbol of the subframe 501 (e.g.,corresponding to time segment or duration t₆) when a neighboring basestation 205 has multiplexed positioning reference signal resourceelements 507 into the seventh OFDM symbol of another subframe 502.

Referring now to FIG. 6, such figure depicts alternative exemplarysubframes 601, 602 generated and transmitted by base stations providingcommunication service to service coverage areas adjacent to orneighboring the service coverage area in which the wirelesscommunication device 201 receiving the subframes is located. Similar tothe subframes 501, 502 of FIG. 5, each of the subframes 601, 602 of FIG.6 includes a control channel portion in which are multiplexed resourceelements 603, 606 containing control information (e.g., resourceelements corresponding to PDCCH, physical control format indicatorchannel (PCFICH), and/or physical HARQ indicator channel (PHICH)) andcell-specific reference symbols and a non-control channel portion inwhich are multiplexed resource elements 604-605, 607-608 containing apositioning reference signal, optional cell-specific reference signaland optional data. As with the subframes 501, 502 of FIG. 5, the OFDMsymbols carrying the positioning reference signal resource elements 604,607 occupy only a portion (i.e., less than all) of the non-controlchannel portion of the subframe 601, 602. However, in contrast to thesubframes 501, 502 depicted in FIG. 5, which illustrate the multiplexingof positioning reference signal resource elements 504, 507 into a singleOFDM symbol in the non-control channel portion of each subframe 501,502, the subframes 601, 602 of FIG. 6 illustrate the multiplexing ofpositioning reference signal resource elements 604, 607 into two OFDMsymbols of each subframe 601, 602 so as to maintain orthogonality of theOFDM symbols. Similar to the subframes 501, 502 of FIG. 5, the OFDMsymbols carrying the positioning reference signal resource elements 604,607 are multiplexed into different OFDM symbols of each subframe 601,602. For example, as illustrated in FIG. 6, positioning reference signalresource elements 604 are multiplexed or mapped into the fifth and ninthOFDM symbols of subframe 601 for transmission from one of theneighboring base stations (e.g., base station 203) and positioningreference signal resource elements 607 are multiplexed or mapped intothe third and seventh OFDM symbols of subframe 602 for transmission fromanother one of the neighboring base stations (e.g., base station 205).Thus, in this embodiment as in the embodiment of FIG. 5, the OFDMsymbols carrying positioning reference signal resource elements 604, 607are separated by at least one OFDM symbol.

Additionally, as in the subframes 501, 503 of FIG. 5, each OFDM symbolcarrying positioning reference signal resource elements 604, 607 isneighbored by at least one OFDM symbol containing blank or emptyresource elements 609, 610 to aid in maintaining orthogonality of theOFDM symbols carrying positioning reference signal resource elements604, 607 when the sum of the propagation delay between the base stationtransmitters 312 and the multipath delay spread of the propagationchannel exceeds the cyclic prefix length associated with the OFDMsymbols carrying the positioning reference signal resource elements 604,607. Further, in one embodiment, blank or empty resource elements 609,610 may be multiplexed into an OFDM symbol corresponding to the OFDMsymbol carrying a positioning reference signal of a neighboring basestation. For example, one base station 203 may multiplex empty resourceelements 609 into the third and seventh OFDM symbols of the subframe 601(e.g., corresponding to time segments or durations t₂ and t₆) when aneighboring base station 205 has multiplexed positioning referencesignal resource elements 607 into the third and seventh OFDM symbols ofanother subframe 602. When the base station processors 316 areprogrammed to add channel-coded data bits to the subframe 601, 602, theresource element 605, 608 containing such data may be multiplexed intoOFDM symbols that are not used for communicating control information orpositioning reference signals. For example, as illustrated in FIG. 6,data resource elements 605, 608 are multiplexed into the last five OFDMsymbols (i.e., corresponding to time segments t₉ through t₁₃) of eachsubframe 601, 602. In alternative embodiments either no OFDM symbol maybe allocated for data transmission or a different number of OFDM symbolsmay be allocated for data transmission. The portion of the non-controlregion that may contain data transmission may be pre-determined (e.g.,specified in a 3GPP specification) or indicated to the UE insemi-statically in a broadcast message (e.g., master information blockor system information block) or through higher layer signaling.

FIG. 7 illustrates further exemplary subframes 701, 702 generated andtransmitted by base stations providing communication service to servicecoverage areas adjacent to or neighboring the service coverage area inwhich the wireless communication device 201 receiving the subframes islocated. Similar to the subframes 501-502, 601-602 of FIGS. 5 and 6,each of the subframes 701, 702 of FIG. 7 includes a control channelportion in which are multiplexed resource elements 703, 706 optionallycontaining control information bits and cell-specific reference signaland other control information, and a non-control channel portion inwhich are multiplexed resource elements 704-705, 707-708 containing apositioning reference signal, optional data, and other optionalinformation (e.g., cell-specific reference signal, synchronizationchannel, physical broadcast channel, etc.).

Similar to the subframes 501, 502 of FIG. 5, the subframes 701, 702illustrated in FIG. 7 include a single OFDM symbol into which has beenmultiplexed positioning reference symbol resource elements 704, 707. Insubframes 701 and 702, the positioning reference signal resourceelements 704, 707 are multiplexed onto a subset of the subcarriersforming the OFDM symbols carrying them. For example, in the embodimentdepicted in FIG. 7, the positioning reference signal resource elements704 are multiplexed onto one-half of the subcarriers forming the OFDMsymbol carrying the positioning reference signal. As illustrated in FIG.7, the positioning reference signal resource elements 704 in subframe701 are multiplexed onto the second, fourth, sixth, eighth, tenth, andtwelfth subcarriers (sub₁, sub₃, sub₅, sub₇, sub₉, sub₁₁) of the OFDMsymbol corresponding to a particular time segment (e.g., t₃); whereas,the positioning reference signal resource elements 707 in subframe 702are multiplexed onto the first, third, fifth, seventh, ninth, andeleventh subcarriers (sub₀, sub₂, sub₄, sub₆, sub₈, sub₁₀) at the sametime segment (e.g., t₃). Thus, instead of arranging the positioningreference signal resource elements so as to be orthogonal in time as inthe subframes 501-502, 601-603 of FIGS. 6 and 7, the subframes 701, 702of FIG. 7 illustrate frequency orthogonality through use of subsets ofsubcarriers to convey the positioning reference signals. Suchorthogonality can be achieved through use of a subset of alternatingsubcarriers as illustrated in FIG. 7 or alternatively through use of asubset of adjacent subcarriers or alternatively through a subset ofalternating blocks of contiguous subcarriers (e.g., alternating resourceblocks). To illustrate the latter alternative, positioning referencesignal resource elements 704 in subframe 701 may be multiplexed onto thefirst through sixth subcarriers (subo through sub₅) of the OFDM symbolcorresponding to a particular time segment (e.g., t₃), while thepositioning reference signal resource elements 707 in subframe 702 maybe multiplexed onto the seventh through twelfth subcarriers (sub₆through sub₁₁) at the same time segment (e.g., t₃). The forgoingexamples illustrate how two base station processors 316 can coordinateand share time-frequency resources within the subframe 701, 702 in anon-overlapping fashion with a pre-determined time-frequency re-use. Inanother example, the entire subframe bandwidth can subdivided intoblocks of six physical resource blocks (PRBs). P/S-SCH extensiontechniques can then be applied here to map the P/S-SCH sequences to eachgroup of six PRBs but across multiple OFDM symbols. Whether or not acertain base station 203, 205 uses a six PRB segment on a particularsymbol can be determined as a function of an identifier, such as a PCIDor cell site ID or some other identifier associated with the basestation 203, 205. In one embodiment, two OFDM symbols are collapsed intoone where the second constituent OFDM symbol is a cyclically shiftedversion of the first constituent symbol before the respective CP of theconstituent symbols are appended. The subframes 701, 702 of FIG. 7illustrate transmission of an OFDM symbol with a duration that is twicethe duration corresponding to either a normal CP OFDM symbol or anextended CP OFDM symbol. In an alternative embodiment, only a portion oftwice the duration may be used for transmission with a transmission gapbefore and/or after OFDM symbol.

As discussed above and unlike the subframe structure of ContributionR1-090353 to 3GPP RAN1, the positioning reference signal resourceelements 704, 707 occupy only a portion (i.e., less than all) of the setof OFDM symbols forming the non-control channel portion of the subframe701, 702. When resource elements 705, 708 containing channel-coded databits are included, such resource elements 705, 708 may be multiplexedinto OFDM symbols that are not used to convey control information orpositioning reference signals. In the embodiment illustrated in FIG. 7,data resource elements 705, 708 are multiplexed into the last five OFDMsymbols of the subframe 701, 702, although the data resource elements705, 708 may be alternatively multiplexed into other OFDM symbols of thesubframe 701, 702. In an alternative embodiments, either no OFDM symbolmay be allocated for data transmission or a different number of OFDMsymbols may be allocated for data transmission. The portion of thenon-control region that may contain data transmission may bepre-determined (e.g., specified in a 3GPP specification) or indicated tothe UE in semi-statically in a broadcast message (e.g., masterinformation block or system information block) or through higher layersignaling.

In addition to providing frequency orthogonality, the base stationprocessors 316 may increase the duration of and/or cyclic prefixassociated with the OFDM symbols used to convey the positioningreference signals. For example, two normal OFDM symbol durations can becollapsed into one and the new duration symbol can be used to transmitan OFDM symbol with a longer cyclic prefix (e.g., 25 microseconds) thanthe normal and/or extended cyclic prefixes (about 5 microseconds and16.67 microseconds, respectively) provided under the E-UTRA standard. Inthis case, the positioning reference signals may be especially designedto comport with the extended duration OFDM symbols. FIG. 7 illustratesuse of one extended duration OFDM symbol in each subframe 701, 702 toconvey the positioning reference signal. As illustrated, the duration ofthe OFDM symbol or symbols carrying the positioning reference signal isgreater than a duration of the remaining OFDM symbols of at least thenon-control channel portion of the subframe 701, 702 that may be usedfor transmission. In an alternative embodiment, the duration of the OFDMsymbol or symbols carrying the positioning reference signal is greaterthan a duration of the OFDM symbols of the control channel portion ofthe subframe 701, 702. Alternatively, multiple extended duration and/orextended cyclic prefix OFDM symbols may be used per subframe 701, 702 tocarry the positioning reference signal with a predeterminedtime-frequency reuse. The use of extended duration OFDM symbols toconvey the positioning reference signals provide an alternativemechanism for mitigating the effects of downlink channel delay spreadwhen such delay spread exceeds the normal or extended cyclic prefixes ofOFDM symbols as provided under the E-UTRA standard. As in the subframestructures illustrated in FIGS. 5 and 6, one or more empty or blank OFDMsymbols may be arranged temporally adjacent the OFDM symbols carryingthe positioning reference signals. Such symbols, when included, may bepopulated with empty or blank resource elements 709, 710.

Those of ordinary skill in the art will readily appreciate and recognizethat various other time and frequency re-use approaches forcommunicating positioning reference signals in overlapping ornon-overlapping time resources can be envisioned taking into account theprinciples described herein and particularly above with respect to thesubframe structures illustrated in FIGS. 5-7. Accordingly, the exemplarysubframe structures discussed above with respect to FIGS. 5-7 are merelyillustrative in nature and should not be construed or used to limit thepresent invention as defined by the appended claims.

Referring now to FIGS. 2, 3 and 5-8, operation of an exemplary wirelesscommunication device 201 to process subframes (e.g., 501, 505, 601, 605,701, 705) containing positioning reference signals in accordance withone embodiment of the present invention will be described. Prior toreceipt of subframes containing positioning reference signals, thewireless device receiver 327 receives (801), from a base station servingthe service coverage area in which the wireless device 201 is located(serving base station), one or more identifiers associated with the basestations that will be transmitting the subframes, particularlyidentifiers associated with base stations serving service coverage areas(e.g., cells or sectors) neighboring the service coverage area in whichthe wireless communication device 201 is presently located. Theidentifiers may be, for example, beacon codes or identifiers, offsetidentifiers, base station identifiers, cell site identifiers, PCIDs,GCIDs, subframe indexes, SFNs, and/or a RNTIs and may have been receivedas part of a broadcast control message, such as an MIB or SIB, from theserving base station. For example, the identifiers associated with thebase stations 203, 205 serving neighboring service coverage areas mayhave been communicated as part of a neighbor cell list transmitted fromthe wireless device's serving base station 204 (assuming, for example,that the wireless device 201 is being serviced by base station 204 inFIG. 2). Alternatively, the identifier may be encoded into a subframecontaining the positioning reference signal (e.g., PDCCH or othercontrol information contained in the subframe).

In addition to receiving identifiers associated with base stationsserving neighboring service coverage areas (neighbor base stations), thewireless communication device receiver 327 receives (803) one or moresubframes containing positioning reference signals from one or more basestations (e.g., base stations 203 and 205). For example, the wirelessdevice 201 may receive a subframe as illustrated in FIGS. 5-7. Thereceiver 327 provides a baseband version of the received subframe to theprocessor 329 for processing in accordance with the present invention.The processor 329 first extracts a base station identifier or anotheridentifier associated with the base station before it can receive thesubframe bearing the positioning reference signal. For example, in theexemplary subframes 501-502, 601-602, and 701-702 of FIGS. 5-7, theprocessor 329 decodes the resource elements in a system broadcastmessage (e.g., system information block) to determine the identifierassociated with the transmitting base station. The processor 329 mayreceive the identifier together with a neighbor cell list or other listof identifiers associated with neighbor base stations.

Upon receiving the subframe, the wireless device processor 329determines (805) whether the subframe originated from a base stationfrom which the wireless device processor 329 can process a positioningreference signal to estimate timing information (e.g., time of arrivalinformation) useful in determining a location of the wireless device 201and whether the subframe contains a positioning reference signal. Thepositioning reference signal may not be transmitted on all subframes,but rather may be transmitted in a certain subset of all subframes usedfor transmission by the base station. The base station may indicate tothe wireless device 201 which subframes bear the positioning referencesignal. The base station may indicate which subframes are used forpositioning reference signal transmission through a second identifierassociated with the base station. This second identifier may bepre-determined (e.g., specified in a 3GPP specification), or alternatelyincluded in a system broadcast message or a UE-specific control message(e.g., radio resource control measurement configuration message) by thebase station. Subsequently, the wireless device processor 329 candetermine whether a subframe contains a positioning reference signal ornot. Further, it can process a positioning reference signal on subframesthat carry such a signal to estimate timing information (e.g., time ofarrival of the first multipath component from the base station) usefulin determining a location of the wireless device 201. When eitheridentifier indicates that either the subframe does not contain aposition reference signal or that the information within the subframe(e.g., a positioning reference signal) cannot be used for determiningposition-related timing information (e.g., the identifier does notcorrespond to a desired base station), the processor 329 ignores (807)the received subframe. On the other hand, when the identifier indicatesthat information within the subframe (e.g., a positioning referencesignal) can be used for determining position-related timing information(e.g., the identifier is on a previously received neighbor cell list),the processor 329 processes the subframe and particular sets oftransmission resources therein to ultimately estimate timing information(e.g., time of arrival or observed time difference of arrivalinformation) that may be used in determining a location of the wirelessdevice 201.

In the event that the received subframe is from a base station fromwhich position-related timing information can be determined, thewireless device processor 329 determines (809) a set of transmissionresources in a non-control channel portion of the received subframe inwhich a positioning reference signal (e.g., an OTDOA waveform) wastransmitted based on an identifier associated with the base station. Forexample, the wireless device memory 331 may store a table that mapsidentifiers with OFDM symbol positions and characteristics (e.g., symboldurations and/or associated cyclic prefixes). The table may be updatedeach time the wireless device 201 receives a new neighbor cell list fromthe currently serving site or cell or when a new cell is detected andthe neighbor cell list is updated by the wireless device 201 in anautonomous fashion.

Based on the identifier (e.g., PCID) associated with the base stationfrom which the subframe was received, the wireless device processor 329demultiplexes the subframe to extract the set of transmission resources(e.g., time-frequency resource elements) carrying the positioningreference signal. In other words, based on the identifier associatedwith the base station that transmitted the subframe and the symbolmapping stored in the wireless device memory 331, the processor 329determines which OFDM symbol or symbols in the non-control channelportion of the frame contains the positioning reference signal.Additionally, the processor 329 determines, based on the stored mapping,whether the OFDM symbol or symbols containing the positioning referencesignal are of normal duration or normal or extended cyclic prefix underthe E-UTRA or LTE standard or have a special duration or associatedcyclic prefix (e.g., a multiple of a normal duration or a special,lengthier cyclic prefix). The processor 329 then processes (811) the setof transmission resources containing the positioning reference signal toestimate time of arrival information associated with the positioningreference signal based on reference timing information. For example, thewireless device processor 329 may determine a time of arrival of thepositioning reference signal based on a reference time or clock suppliedby the wireless device's local oscillator 332. Further, the wirelessdevice processor 329 may determine time of arrival from at least twobase stations from their respective positioning reference signaltransmissions based on a reference clock. In addition, the deviceprocessor 329 may compute the time difference of arrival correspondingto at least a subset of those base stations with the time of arrival ofone base station as the reference.

In one embodiment, after the transmission resources containing thepositioning reference signal have been processed and the timinginformation estimated, the wireless device processor 329 may determine(813) whether the wireless device 201 is in an autonomous locationdetermining mode in which the wireless device processor 329 determinesthe wireless device's location. If the wireless device 201 is in such anautonomous location mode, the wireless device processor 329 determines(815) the wireless device's location based on the timing informationcomputed for subframes received from multiple (two or more) basestations serving neighboring service coverage areas. In this case, thewireless device memory 331 stores the fixed locations of the system basestations and uses those fixed locations together with time of arrivalinformation to determine its location using known triangulation ortrilateration methods. Alternatively, if the wireless device 201 is notin an autonomous location determining mode and its location is to bedetermined by another device, such as the wireless system's locationserver 207, the wireless device communicates (817) the timinginformation (e.g., estimated times of arrival of positioning referencesignals received from two or more neighbor base stations) to thelocation-determining device via the wireless device's serving basestation.

The wireless device in 201 may identify newly detectable cells on acertain carrier frequency autonomously and send a measurement report toa base station that it is connected to. Alternately, the base stationmay send a neighbor cell list re-configuration message to the UE. Eitherway, the wireless device 201 may update its neighbor cell list. A thebase station may send a UE-specific configuration message (e.g., radioresource control measurement configuration message) requesting thewireless device 201 to determine the observed time difference of arrivalcorresponding to a subset of the neighboring base stations and reportthem. When the wireless device 201 may receive and decode such a messageand in response to it, determine the observed time difference of arrivalcorresponding to the subset of the configured neighboring base stations.The wireless device may then report these measurements to the basestation it is connected to.

To provide a further example of the operation of the wireless deviceprocessor 329 to assist in determining the wireless device's location,consider the system 200 of FIG. 2 under the circumstances in which basestation 204 is providing wireless service to the wireless device 201 andbase stations 203 and 205 are providing wireless service to servicecoverage areas (e.g., cells or sectors) neighboring the service coveragearea serviced by base station 204. In this case, the wireless device mayreceive subframes from both neighbor base stations 203, 205 (e.g.,subframes configured as illustrated in FIG. 5, FIG. 6, or FIG. 7). Inthis embodiment, each subframe includes a one millisecond (1 ms) blockof resource elements that are divided in time across a group ofsubcarriers to form OFDM symbols. Each resource element occupies apredetermined amount of time (e.g., about 70 microseconds) on itsrespective subcarrier. The OFDM symbols of each subframe are arrangedinto a first set of OFDM symbols into which control information has beenencoded and a second set of OFDM symbols into which information otherthan control information has been encoded. Such other informationincludes a positioning reference signal and, optionally, data. In otherwords, each subframe may be configured to support a control channel(e.g., PDCCH), a synchronization channel (e.g., a P/S-SCH), and a datachannel (e.g., a PDSCH).

After receiving the subframes, the wireless device processor 329determines, for each subframe, a set of resource elements (andanalogously a set of OFDM symbols) in which a positioning referencesignal was transmitted based on an identifier associated with the basestation 203, 205 from which the particular subframe was received. Theset of OFDM symbols carrying the positioning reference signal from basestation 203 is preferably orthogonal to the set of OFDM symbols carryingthe positioning reference signal from base station 205. To increase thelikelihood that such OFDM symbols remain orthogonal during unfavorabledownlink channel conditions, such as when the overall delay spread ofthe downlink channel (i.e., propagation delay plus multipath delayspread) as seen from the wireless device 201 exceeds a cyclic prefix(CP) length for normal CP (approximately five microseconds) or extendedCP (approximately 16.67 microseconds) as provided under the E-UTRAstandard, each subframe may include one or more blank or empty OFDMsymbols positioned adjacent the OFDM symbols carrying the positioningreference signals such that the OFDM symbols carrying the positioningreference signals are different for each base station 203, 205 (e.g., asillustrated in FIG. 5 or FIG. 6). Alternatively, instead of separatingthe OFDM symbols in time between neighboring base stations 203, 205, theresource elements containing the positioning reference signal may bearranged within one or more common OFDM symbols such that there isfrequency separation between the positioning reference signal resourceelements (e.g., as illustrated in FIG. 7). In the latter case, theduration of the OFDM symbols carrying the positioning reference signalmay be increased as compared to the duration of other OFDM symbols inthe non-control channel portion of the subframe. In either event, theOFDM symbol or symbols carrying the positioning reference signal in eachsubframe occupy only a portion (less than all) of the OFDM symbols inthe non-control channel portion of the subframe.

The difference in positioning of the positioning reference signalresource elements and/or OFDM symbols either in time or frequency isstored in the wireless device memory 331 and may be updated on a regularbasis in connection with receipt of updated neighbor cell lists from theserving base station 204. As a result, the wireless device processor 329may map the identifier of the base station 203, 205 that transmitted thesubframe to the stored information mapping identifiers associated withbase stations to positioning of resource elements and/or OFDM symbolscarrying positioning reference signals to determine the location and/orcharacteristics (e.g., duration and/or cyclic prefix) of such resourceelements and/or OFDM symbols within a particular received subframe.

After the wireless processor 329 has determined the sets of resourceelements in which the positioning reference signals were transmitted inthe subframes received from the base stations 203, 205 based onidentifiers associated with the base stations 203, 205, the wirelessdevice processor 329 processes the sets of resource elements to estimatetimes of arrival of the respective positioning reference signals basedon a local oscillator frequency of the wireless device's localoscillator 332. The wireless device processor 329 then provides theestimated times of arrival in an message (e.g., in a radio resourcecontrol measurement report message transmitted by the wireless device201 on the uplink) to the wireless device transmitter 325 fortransmission to the serving base station 204 and ultimatelycommunication to the location server 207 for determination of thewireless device's location. Alternatively, as discussed above, when thewireless device processor 329 has been programmed to autonomouslyestimate the wireless device's location, the wireless device processor329 may compute its own location based on the estimated times of arrivaland other information as may be provided to the wireless device 201and/or stored in the wireless device memory 331 (e.g., base stationlocations, transmission times of the subframes, channel conditions, andso forth as is known in the art).

The instructions illustrated in FIG. 7 for controlling operation of thebase station processor 316 (e.g., 401-413) logic flow blocks may beimplemented as programming instructions, which are stored in basestation memory 318 and executed at appropriate times by the base stationprocessor 316. Similarly, the instructions illustrated in FIG. 8 forcontrolling operation of the wireless device processor 329 (e.g., logicflow blocks 805-815) may be implemented as programming instructions,which are stored in wireless device memory 331 and executed atappropriate times by the wireless device processor 329.

The present invention encompasses an apparatus and method forcommunicating positioning reference signals based on an identifierassociated with a base station. With this invention, orthogonality ofOFDM symbols carrying positioning reference signals which have beentransmitted by base stations of neighboring cells or sectors ismaintained even under conditions causing substantial downlink channeldelay spread as perceived by a wireless device. By utilizing less thanall of the OFDM symbols in the non-control channel portion of a downlinksubframe to convey the positioning reference signal, empty OFDM symbolsare made available to absorb the effects of delay spreads that aregreater than the cyclic prefix of the OFDM symbols carrying the positionreference signals, thereby maintaining the orthogonality of DFTprecoding. Alternatively, by increasing the duration of or cyclic prefixassociated with the OFDM symbol or symbols carrying the positioningreference signal, such increase in duration or cyclic prefix offsetsincreased delay spreads incurred under various network conditions andenables the orthogonality of DFT preceding to be maintained. Identifiersassociated with the base stations transmitting the subframes are used bythe wireless communication device to indicate the positioning and/orcharacteristics of resource elements and/or associated OFDM symbolscarrying a positioning reference signal within a subframe to facilitatethe maintenance of orthogonality while insuring proper demultiplexingand subsequent processing of the resource elements.

As detailed above, embodiments of the present invention reside primarilyin combinations of method steps and apparatus components related tocommunicating positioning reference signals to aid in determining ageographic location of a wireless communication device. Accordingly, theapparatus components and method steps have been represented, whereappropriate, by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments ofthe present invention so as not to obscure the disclosure with detailsthat will be readily apparent to those of ordinary skill in the arthaving the benefit of the description herein.

In this document, relational terms such as “first” and “second,” “top”and “bottom,” and the like may be used solely to distinguish one entityor action from another entity or action without necessarily requiring orimplying any actual such relationship or order between such entities oractions. The terms “comprises,” “comprising,” and any other variationsthereof are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus. The term “plurality of” as used in connection with any objector action means two or more of such object or action. A claim elementproceeded by the article “a” or “an” does not, without more constraints,preclude the existence of additional identical elements in the process,method, article, or apparatus that includes the element.

It will be appreciated that embodiments of the base station 301 and thewireless communication device 201 described herein may be comprised ofone or more conventional processors and unique stored programinstructions that control the processor(s) to implement, in conjunctionwith certain non-processor circuits, some, most, or all of the functionsof the base station 301 and the wireless communication device 201 andtheir operational methods as described herein. The non-processorcircuits may include, but are not limited to, the transmitters 312, 325,the receivers 314, 327, the antennas 304-307, 39-310, 320, 322-323, thelocal oscillator 332, the display 333, the user interface 335, memory318, 331, and the alerting mechanism 337 described above, as well asfilters, signal drivers, clock circuits, power source circuits, userinput devices, and various other non-processor circuits. As such, thefunctions of these non-processor circuits may be interpreted as steps ofa method in accordance with one or more embodiments of the presentinvention. Alternatively, some or all functions could be implemented bya state machine that has no stored program instructions, or in one ormore application specific integrated circuits (ASICs), in which eachfunction or some combinations of certain of the functions areimplemented as custom logic. Of course, a combination of the twoapproaches could be used. Thus, methods and means for these functionshave been generally described herein. Further, it is expected that oneof ordinary skill, notwithstanding possibly significant effort and manydesign choices motivated by, for example, available time, currenttechnology, and economic considerations, when guided by the concepts andprinciples disclosed herein will be readily capable of generating suchsoftware instructions or programs and integrated circuits without undueexperimentation.

In the foregoing specification, specific embodiments of the presentinvention have been described. However, one of ordinary skill in the artwill appreciate that various modifications and changes can be madewithout departing from the scope of the present invention as set forthin the claims below. Accordingly, the specification and figures are tobe regarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofpresent invention. The benefits, advantages, solutions to problems, andany element(s) that may cause any benefit, advantage, or solution tooccur or become more pronounced are not to be construed as critical,required, or essential features or elements of any or all the claims.The invention is defined solely by the appended claims including anyamendments made during the pendency of this application and allequivalents of those claims as issued.

1. A wireless communication device operable in a wireless communicationsystem that includes at least one base station, the wirelesscommunication device comprising: a receiver operable to receive at leasta section of a subframe from a base station, the subframe including aplurality of transmission resources multiplexed onto subcarriers of aplurality of orthogonal frequency division multiplexed (OFDM) symbols,each transmission resource of the plurality of transmission resourcesoccupying a predetermined amount of time on a respective one of thesubcarriers, the plurality of OFDM symbols being arranged into at leasta first set of OFDM symbols that includes a positioning reference signaland a second set of OFDM symbols that does not include the positioningreference signal; and a processor operably coupled to the receiver, theprocessor operable to: determine, based on an identifier associated withthe base station, a set of transmission resources over which thepositioning reference signal was transmitted, the set of transmissionresources constituting at least a portion of the first set of OFDMsymbols; and process the set of transmission resources to estimatetiming information associated with the positioning reference signal. 2.The wireless communication device of claim 1, wherein the processor isfurther operable to: determine a time of arrival of the positioningreference signal based on reference timing information and the estimatedtiming information.
 3. The wireless communication device of claim 2,wherein the receiver is operable to receive transmissions from aplurality of base stations, the wireless communication device furthercomprising: a transmitter operably coupled to the processor and operableto communicate at least the time of arrival to at least one of theplurality of base stations.
 4. The wireless communication device ofclaim 1, wherein the subframe forms part of a radio frame and whereinthe processor is further operable to: determine, based on theidentifier, whether the subframe includes transmission resourcescorresponding to the positioning reference signal prior to determiningthe set of transmission resources.
 5. The wireless communication deviceof claim 1, wherein a cyclic prefix associated with each OFDM symbol inthe portion of the first set of OFDM symbols is identical.
 6. Thewireless communication device of claim 1, wherein the first set of OFDMsymbols includes at least a first subset of OFDM symbols and a secondsubset of OFDM symbols, wherein the set of transmission resources formthe first subset of OFDM symbols, and wherein a duration of each OFDMsymbol of the first subset of OFDM symbols is greater than a duration ofeach OFDM symbol of the second set of OFDM symbols.
 7. The wirelesscommunication device of claim 6, wherein a cyclic prefix associated witheach OFDM symbol of the first subset of OFDM symbols is greater than16.67 microseconds.
 8. The wireless communication device of claim 1,wherein the identifier is derived from at least one of an offsetidentifier, a cell site identifier, a physical cell identifier, a globalcell identifier, a symbol index, a slot index, a subframe index, asystem frame number, and a radio network transaction identifier.
 9. Thewireless communication device of claim 8, wherein the identifierassociated with the base station is identical to identifiers associatedwith a plurality of other base stations.
 10. The wireless communicationdevice of claim 9, wherein the base station and the plurality of otherbase stations are co-located. 11-21. (canceled)
 22. A method for awireless communication device to at least determine position-relatedtiming information, the wireless communication device operating in awireless communication system that includes a plurality of basestations, the method comprising: receiving at least a section of asubframe transmitted by a first base station of the plurality of basestations, the subframe including a plurality of transmission resourcesmultiplexed onto subcarriers of a plurality of orthogonal frequencydivision multiplexed (OFDM) symbols, each transmission resource of theplurality of transmission resources occupying a predetermined amount oftime on a respective one of the subcarriers, the plurality of OFDMsymbols being arranged into a first set of OFDM symbols that includes apositioning reference signal and a second set of OFDM symbols that doesnot include a positioning reference signal; determining, based on anidentifier associated with the first base station, a set of transmissionresources over which the positioning reference signal was transmitted,the set of transmission resources constituting a portion of the firstset of OFDM symbols; and processing the set of transmission resources toestimate timing information associated with the positioning referencesignal.
 23. The method of claim 22, further comprising: determining atime of arrival of the positioning reference signal based on referencetiming information and the estimated timing information.
 24. The methodof claim 23, further comprising: communicating at least the time ofarrival to at least one of the plurality of base stations.
 25. Themethod of claim 22, wherein each of the plurality of base stationsprovides wireless communication service within a respective servicecoverage area, the method further comprising: receiving the identifierfrom a second base station prior to receipt of the subframe from thefirst base station.
 26. The method of claim 25, wherein receiving theidentifier comprises: receiving a list of identifiers associated atleast some of the plurality of base stations.
 27. The wirelesscommunication device of claim 25, wherein receiving the identifiercomprises: receiving the identifier in a broadcast message from thesecond base station.
 28. (canceled)
 29. A method for a wirelesscommunication device to determine time of arrival information from whicha location of the wireless communication device may be estimated, thewireless communication device operating in a wireless communicationsystem that includes a plurality of base stations and a location server,each of the plurality of base stations providing wireless communicationservice within a respective service coverage area, the location serverbeing operable to determine locations of wireless communication deviceswithin a coverage area of the wireless communication system, thewireless communication device receiving wireless communication servicefrom a first base station of the plurality of base stations, the methodcomprising: receiving a first subframe transmitted by a second basestation of the plurality of base stations, the first subframe includinga first plurality of resource elements that are divided in time across afirst plurality of subcarriers to form a first plurality of orthogonalfrequency division multiplexed (OFDM) symbols, each resource element ofthe first plurality of resource elements occupying a predeterminedamount of time on a respective one of the first plurality ofsubcarriers, the first plurality of OFDM symbols being arranged into afirst set of OFDM symbols that includes a first positioning referencesignal and a second set of OFDM symbols that does not include the firstpositioning reference signal; receiving a second subframe transmitted bya third base station of the plurality of base stations, the secondsubframe including a second plurality of resource elements that aredivided in time across a second plurality of subcarriers to form asecond plurality of orthogonal frequency division multiplexed (OFDM)symbols, each resource element of the second plurality of resourceelements occupying a predetermined amount of time on a respective one ofthe second plurality of subcarriers, the second plurality of OFDMsymbols being arranged into a third set of OFDM symbols that includes asecond positioning reference signal and a fourth set of OFDM symbolsthat does not include the second positioning reference signal;determining, based on an identifier associated with the second basestation, a first set of resource elements over which the firstpositioning reference signal was transmitted in the first subframe, thefirst set of resource elements constituting a portion of the first setof OFDM symbols; determining, based on an identifier associated with thethird base station, a second set of resource elements over which thesecond positioning reference signal was transmitted in the secondsubframe, the second set of resource elements constituting a portion ofthe third set of OFDM symbols, wherein the portion of the third set ofOFDM symbols containing the second positioning reference signal isdifferent than and orthogonal to the portion of the first set of OFDMsymbols containing the first positioning reference signal; processingthe first set of resource elements to estimate a first time of arrivalof the first positioning reference signal based on a local oscillatorfrequency of the wireless communication device; processing the secondset of resource elements to estimate a second time of arrival of thesecond positioning reference signal based on the local oscillatorfrequency; and communicating the first time of arrival and the secondtime of arrival to the location server via the first base station.
 30. Amethod for a wireless communication device to at least determineposition-related timing information, the wireless communication deviceoperating in a wireless communication system that includes a pluralityof base stations, the method comprising: receiving at least a section ofa subframe transmitted by a first base station of the plurality of basestations, the subframe including a plurality of transmission resourcesmultiplexed onto subcarriers of a plurality of orthogonal frequencydivision multiplexed symbols, each transmission resource of theplurality of transmission resources occupying a predetermined amount oftime on a respective one of the subcarriers, the plurality oftransmission resources being arranged into at least a first set oftransmission resources that includes a positioning reference signal anda second set of transmission resources that includes channel-coded data,the second set of transmission resources being different than the firstset of transmission resources; determining, based on an identifierassociated with the first base station, the first set of transmissionresources over which the positioning reference signal was transmitted;determining the second set of transmission resources over which thechannel-coded data was transmitted; processing the first set oftransmission resources to estimate timing information associated withthe positioning reference signal; and processing the second set oftransmission resources to recover the channel-coded data.
 31. The methodof claim 30, wherein the plurality of transmission resources includes athird set of transmission resources over which at least one of controlinformation, synchronization information, and one or more additionalreference signals was transmitted, the third set of transmissionresources being different than the first set of transmission resourcesand the second set of transmission resources, the method furthercomprising: determining the third set of transmission resources overwhich at least one of control information, synchronization information,and one or more additional reference signals was transmitted; andprocessing the third set of transmission resources to recover the atleast one of control information, synchronization information, and oneor more additional reference signals.
 32. The method of claim 31,wherein the at least one of control information, synchronizationinformation, and one or more additional reference signals includes atleast one of a physical downlink control channel (PDDCH), a physicalcontrol format indicator channel (PCFICH), a physical hybrid automaticrepeat request indicator channel (PHICH), a broadcast channel, asynchronization channel, a cell-specific reference signal, and a userequipment (UE) specific reference signal.
 33. The method of claim 30,wherein the identifier is derived from at least one of an offsetidentifier, a cell site identifier, a physical cell identifier, a globalcell identifier, a symbol index, a slot index, a subframe index, asystem frame number, and a radio network transaction identifier.
 34. Themethod of claim 33, wherein the offset identifier is used to derive astarting point offset for extracting a subsequence of a referencequadrature phase shift keying (QPSK) sequence.
 35. A wirelesscommunication device operable in a wireless communication system thatincludes at least one base station, the wireless communication devicecomprising: a receiver operable to receive at least a section of asubframe from a base station, the subframe including a plurality oftransmission resources multiplexed onto subcarriers of a plurality oforthogonal frequency division multiplexed (OFDM) symbols, eachtransmission resource of the plurality of transmission resourcesoccupying a predetermined amount of time on a respective one of thesubcarriers, the plurality of transmission resources being arranged intoat least a first set of transmission resources that includes apositioning reference signal and a second set of transmission resourcesthat includes channel-coded data, the second set of transmissionresources being different than the first set of transmission resources;and a processor operably coupled to the receiver, the processor operableto: determine, based on an identifier associated with the base station,the first set of transmission resources over which the positioningreference signal was transmitted; determining the second set oftransmission resources over which the channel-coded data wastransmitted; process the set of transmission resources to estimatetiming information associated with the positioning reference signal; andprocess the second set of transmission resources to recover thechannel-coded data.
 36. The wireless communication device of claim 35,wherein the plurality of transmission resources includes a third set oftransmission resources over which at least one of control information,synchronization information, and one or more additional referencesignals was transmitted, the third set of transmission resources beingdifferent than the first set of transmission resources and the secondset of transmission resources, and wherein the processor is furtheroperable to: determine the third set of transmission resources overwhich the at least one of control information, synchronizationinformation, and one or more additional reference signals wastransmitted; and process the third set of transmission resources torecover the at least one of control information, synchronizationinformation, and one or more additional reference signals.
 37. Thewireless communication device of claim 36, wherein the at least one ofcontrol information, synchronization information, and one or moreadditional reference signals includes at least one of a physicaldownlink control channel (PDDCH), a physical control format indicatorchannel (PCFICH), a physical hybrid automatic repeat request indicatorchannel (PHICH), a broadcast channel, a synchronization channel, acell-specific reference signal, and a user equipment (UE) specificreference signal.
 38. The wireless communication device of claim 35,wherein the identifier is derived from at least one of an offsetidentifier, a cell site identifier, a physical cell identifier, a globalcell identifier, a symbol index, a slot index, a subframe index, asystem frame number, and a radio network transaction identifier.
 39. Thewireless communication device of claim 38, wherein the offset identifieris used to derive a starting point offset for extracting a subsequenceof a reference quadrature phase shift keying (QPSK) sequence.